Position determining device for determining the position of an object within a tubular structure

Abstract

The invention relates to a position determining device for determining a position of an elongate object within a tubular structure, said position determining device comprising a first providing unit for providing a first distribution of curvature values at a plurality of first points along a path within the tubular structure. The position determining device further comprises a second providing unit for providing a second distribution of strain values or of curvature values at a plurality of points along the object, and a position determining unit for determining the position of the object relative to the path on the basis of the first and second distributions.

The invention claimed is: 
     
       1. A position determining device for determining a current position of an elongate medical instrument within a tubular structure as the elongate medical instrument is moving, wherein the elongate medical instrument comprises a catheter, a bronchoscope, or a guide wire, said position determining device comprising:
 a first providing unit configured to provide a plurality of first distributions of curvature values for a plurality of paths within the tubular structure, wherein the first providing unit is a storage medium configured to store previously computed values that are the plurality of first distributions of curvature values, is a computer processor configured to execute code that receives the plurality of first distributions of curvature values, or is a computer processor configured to execute code to calculate the plurality of first distributions of curvature values; 
 a second providing unit configured to provide a plurality of second distributions of strain values or curvature values, wherein the second providing unit is a storage medium configured to store previously computed values that are the plurality of second distributions of strain values or curvature values, is a computer processor configured to execute code that receives the plurality of second distributions of strain values or curvature values, or is a computer processor configured to execute code to calculate the plurality of second distributions of strain values or curvature values, and wherein the second providing unit is configured to provide the plurality of second distributions along the elongate medical instrument for different points in time, wherein each of the plurality of second distributions corresponds to a position of the elongate medical instrument relative to a path at a point in time within the tubular structure; and 
 a position determining unit comprising a computer processor configured to execute program code that determines a most plausible position of the elongate medical instrument within one of the plurality of paths on the basis of the provided first and second distributions; 
 wherein the position determining unit is further configured to determine the most plausible position of the elongate medical instrument as the elongate medical instrument is moved within the tubular structure by:
 determining for each respective path of the plurality of paths and for each point in time for a plurality of points in time, a distribution of dissimilarity scores for different candidate positions of the elongate medical instrument relative to the respective path by applying a dissimilarity measure to a respective first distribution and a respective second distribution, wherein the dissimilarity measure is adapted to return a dissimilarity score indicative of a dissimilarity of the respective first distribution and the respective second distribution, and 
 determining the most plausible position of the elongate medical instrument relative to one of the plurality of paths on the basis of the dissimilarity scores determined for each of the respective different paths, the different points in time and the different candidate positions by determining optimal routes of the elongate medical instrument relative to each of the plurality of paths using route scores based upon the dissimilarity scores and determining which of these optimal routes represents the most plausible position of the elongate medical instrument relative to the one of the plurality of paths, and 
 
 wherein the position determining unit is configured to forward for further processing the most plausible position of the elongate medical instrument as the current position of the elongate medical instrument in one of the plurality of paths in the tubular structure. 
 
     
     
       2. The position determining device of  claim 1 , wherein the plurality of first distributions of curvature values are scalar distributions. 
     
     
       3. The position determining device of  claim 1 , wherein the plurality of second distributions are based upon optical signals from optical strain sensors arranged along the elongate medical instrument. 
     
     
       4. The position determining device of  claim 1 , wherein the dissimilarity scores determined for the different points in time of the plurality of points in time and the different candidate positions for each path of the plurality of paths represent a map, wherein each respective dissimilarity score value in the map corresponds to a different map location specified by the respective point in time and respective candidate position of the elongate medical instrument relative to a respective path, and wherein the determining optimal routes of the elongate medical instrument relative to each of the plurality of paths using route scores based upon the dissimilarity scores and determining which of these optimal routes represents the most plausible position of the elongate medical instrument relative to the one of the plurality of paths further comprises:
 for each path of the plurality of paths, providing a route score associated with each route through the respective map for each path, each route ending at a candidate position of the elongate medical instrument for a latest point in time and beginning at a candidate position of the elongate medical instrument for an earlier point in time, the associated route score depending on the dissimilarity scores along the respective route; 
 determining, for each path of the plurality of paths, a respective optimal route through the respective map by determining a minimum route score for the path based upon the route scores associated with each route through the respective map ; and 
 determining the most plausible position of the elongate medical instrument relative to one of the plurality of paths based on the determined optimal routes. 
 
     
     
       5. The position determining device of  claim 4 , wherein the position determining device is further configured to provide the route scores for each path of the plurality of paths by determining a sum of the dissimilarity scores along each route through each respective map of each path of the plurality of paths. 
     
     
       6. The position determining device of  claim 4 , wherein the determining, for each path of the plurality of paths, the respective optimal route through the respective map and the determining the most plausible position of the elongate medical instrument relative to the one of the plurality of paths based on the determined optimal routes further comprises:
 calculating the optimal routes for a respective path of the plurality of paths at different points in time such that a respective optimal route with a corresponding route score is determined based upon the dissimilarity scores calculated for a particular point in time and for earlier points in time and for the each of the candidate positions along the respective path; 
 selecting at each point in time, from the calculated optimal routes, the optimal route for which the minimum route score has been determined; and 
 specifying the candidate positions defined by the selected optimal route as the position of the elongate medical instrument relative to one of the paths. 
 
     
     
       7. The position determining device of  claim 1 , wherein the position determining unit is configured to apply the dissimilarity measure by:
 determining a spatial first gradient distribution for each of the plurality of first distributions of curvature values; 
 determining a spatial second gradient distribution for each of the plurality of second distributions of strain values or curvature values; 
 comparing, for each location along the elongate medical instrument, a respective spatial second gradient distribution with a respective spatial first gradient distribution, wherein each respective candidate position of the candidate positions defines which respective gradient of the spatial second gradient distribution is compared with which respective gradient of the spatial first gradient distribution at a respective location, wherein the position determining unit is further configured for the respective location and for the respective candidate position, to apply a sub-dissimilarity measure which is dependent a) on the directions of the respective gradient of the spatial second gradient distribution relative to the respective gradient of the spatial first gradient distribution or b) on the amount of the respective gradient of the spatial first gradient distribution and the amount of the respective gradient of the spatial second gradient distribution, and to determine a sub-dissimilarity score for each respective location by applying the sub-dissimilarity measure; and 
 summing the sub-dissimilarity scores determined for each candidate position, in order to determine a respective dissimilarity score for the respective candidate position. 
 
     
     
       8. The position determining device of  claim 1 , wherein the position determining unit is configured to apply the dissimilarity measure to the respective first distribution and the respective second distribution by:
 determining local maxima of the respective first distribution; 
 determining local maxima of the respective second distribution; 
 assigning to each local maximum of the respective first distribution a local maximum of the respective second distribution, so that a sum of all the spatial distances between assigned local maxima is minimal, wherein each local maximum of the respective second distribution is assigned to only one local maximum of the respective first distribution; and 
 adding the spatial distances between the assigned local maxima of the respective first distribution and the assigned local maxima of the second respective distribution. 
 
     
     
       9. The position determining device of  claim 1 , wherein the position determining unit is configured to apply the dissimilarity measure to the respective first distribution and the respective second distribution by:
 comparing a respective value of the respective second distribution with a respective value of the respective first distribution for each location along the elongate medical instrument, wherein the respective candidate position defines which respective value of the second distribution is compared with which respective value of the first distribution at a respective location, wherein, for the respective location and for the respective candidate position, the position determining unit is configured to use a sub-dissimilarity measure which is zero if a) the respective value of the respective first distribution is above a predefined first threshold or b) the respective value of the respective first distribution is below the first threshold and the respective value of the respective second distribution is below a predefined second threshold, and which otherwise has a positive value; and 
 summing the sub-dissimilarity scores determined for a candidate position, in order to determine a respective dissimilarity score for the respective candidate position. 
 
     
     
       10. The position determining device of  claim 1 , wherein the position determining unit is configured to apply the dissimilarity measure to the respective first distribution and the respective second distribution by applying a normalised cross-correlation to the respective first distribution and the respective second distribution for the respective candidate position. 
     
     
       11. The position determining device of  claim 1 , wherein the plurality of second distributions of strain values or curvature values comprises strain values. 
     
     
       12. An imaging system, comprising:
 a position determining device structured to determine the current position of an elongate medical instrument within a tubular structure in accordance with  claim 1 ; 
 an imaging unit structured to provide an image of the tubular structure, wherein the imaging unit is a device configured to provide a computed tomography image, a magnetic resonance imaging image, or an other type of three-dimensional image; and 
 a visualisation generating unit comprising a computer processor configured to execute code that receives the forwarded current position of the elongate medical instrument in one of the plurality of paths and generates a visualisation of the tubular structure on the basis of the image provided and the position determined, showing the current position of the elongate medical instrument in a respective path in the tubular structure based upon the most plausible position determined from the distributions of dissimilarity scores. 
 
     
     
       13. An imaging method, comprising:
 determining an image of a tubular structure; 
 determining the current position of an elongate medical instrument within the tubular structure using a position determining device configured according to  claim 1 ; and 
 generating a visualisation of the tubular structure on the basis of the image provided and the position determined, showing the current position of the elongate medical instrument in a respective path in the tubular structure based upon the most plausible position determined from the distributions of dissimilarity scores. 
 
     
     
       14. A non-transitory computer-readable storage medium containing instructions that, when executed, cause a computer processor of an imaging system to provide an image of a tubular structure and to generate a visualisation of the tubular structure on a basis of the image provided and a current position, by performing a method comprising:
 receiving the image of the tubular structure from an imaging device configured to provide a computed tomography image, a magnetic resonance imaging image, or an other type of three-dimensional image; 
 determining the current position of an elongate medical instrument within the tubular structure using a position determining device configured in accordance with  claim 1 ; and 
 generating a visualisation of the tubular structure on the basis of the image provided and the position determined, showing the current position of the elongate medical instrument in a respective path in the tubular structure based upon the most plausible position determined from the distributions of dissimilarity scores. 
 
     
     
       15. A method for determining a current position of an elongate medical instrument within a tubular structure as the elongate medical instrument is moving, wherein the elongate medical instrument comprises a catheter, a bronchoscope, or a guide wire, comprising:
 under control of one or more computer processors,
 determining, using stored values, received values, or calculated values, a plurality of first distributions of curvature values for a plurality of paths within the tubular structure; 
 determining, using stored values, received values, or calculated values, a plurality of second distributions of strain values or curvature values along the elongate medical instrument, wherein the plurality of second distributions are determined along the elongate medical instrument for different points in time, and wherein the plurality of second distributions correspond to a plurality of positions of the elongate medical instrument relative to a path within the tubular structure; and 
 
 calculating a most plausible position of the elongate medical instrument relative to one of the plurality of paths on the basis of the determined first distribution of curvature values and the determined second distribution of strain values or curvature values as the elongate medical instrument is moved within the tubular structure by:
 determining, for each respective path of the plurality of paths and for each point in time for a plurality of points in time, a distribution of dissimilarity scores for different candidate positions of the elongate medical instrument relative to the respective path by applying a dissimilarity measure to a respective first distribution and a respective second distribution, wherein the dissimilarity measure is adapted to return a dissimilarity score indicative of a dissimilarity of the respective first distribution and the respective second distribution; 
 determining the most plausible position of the elongate medical instrument relative to one of the paths on the basis of the dissimilarity scores determined for each of the plurality of paths, the different points in time and the different candidate positions by determining optimal routes of the elongate medical instrument relative to each of the plurality of paths using route scores based upon the dissimilarity scores and determining which of these optimal routes represents the most plausible position of the elongate medical instrument relative to the one of the plurality of paths; and 
 forwarding for further processing the most plausible position of the elongate medical instrument as the determined current position of the elongate medical instrument in one of the plurality of paths in the tubular structure. 
 
 
     
     
       16. A non-transitory computer-readable storage medium containing instructions for controlling a computer processor to determine a current position of an elongate medical instrument within a tubular structure as the elongate medical instrument is moving, wherein the elongate medical instrument comprises a catheter, a bronchoscope, or a guide wire, by performing on a position determining device a method comprising:
 determining a plurality of first distributions of curvature values for each of a plurality of paths within the tubular structure; 
 determining a plurality of second distributions of strain values or curvature values along the elongate medical instrument, wherein the plurality of second distributions are determined along the elongate medical instrument for different points in time, and wherein the plurality of second distributions correspond to a plurality of positions of the elongate medical instrument relative to a path within the tubular structure; and 
 calculating a most plausible position of the elongate medical instrument relative to one of the plurality of paths on the basis of the determined first distribution of curvature values and the determined second distribution of strain values or curvature values as the elongate medical instrument is moved within the tubular structure; 
 determining, for each respective path of the plurality of paths and for each point in time for a plurality of points in time, a distribution of dissimilarity scores for different candidate positions of the elongate medical instrument relative to the respective path by applying a dissimilarity measure to a respective first distribution and a respective second distribution, wherein the dissimilarity measure is adapted to return a dissimilarity score indicative of a dissimilarity of the respective first distribution and the respective second distribution; 
 determining the most plausible position of the elongate medical instrument relative to one of the paths on the basis of the dissimilarity scores determined for each of the plurality of paths, the different points in time and the different candidate positions by determining optimal routes of the elongate medical instrument relative to each of the plurality of paths using route scores based upon the dissimilarity scores and determining which of these optimal routes reflects the most plausible position of the elongate medical instrument relative to the one of the plurality of paths; and 
 forwarding for further processing the most plausible position of the elongate medical instrument as the determined current position of the elongate medical instrument in one of the plurality of paths in the tubular structure.